1. Field Of The Invention
This invention relates to apparatus and methods for perforating wells, and more particularly, to a modular gun system and method of use utilizing a plurality of perforating guns which may be individually positioned in a wellbore and individually removed therefrom.
2. Description Of The Prior Art
In the past, tubing conveyed perforating systems for use in completing wells have been conveyed into the wells on a tubing or pipe string with the string left in position in the well during the perforating of the well. After perforating of the well, the perforating guns may have disintegrated or may be retrieved, or may be released or dropped from the tubing or pipe string through the use of various techniques.
More recently, an automatically releasing gun hanger has been proposed as shown in U.S. Pat. No. 5,156,213 to George et al., assigned to the assignee of the present invention. The George et al. `213 patent describes an automatically releasing gun hanger which is run into the well on a rigid tubing string or pipe string. The gun hanger is set within the well by a rotating motion of the rigid tubing string or pipe string. The rigid tubing string or pipe string is then disconnected from the guns attached to the gun hanger through further rotational motion. The pipe string can then be removed from the well. The perforating gun is fired by a pressure actuated firing head and upon firing of the perforating gun, the gun hanger automatically releases, thus allowing the guns to drop to the bottom of the well and leave an unobstructed flow path from the perforations up through the wellbore.
Even more recently, it has been proposed to run the perforating guns into the well on a coiled tubing string. In such cases, rotation of the string is not possible, as with a rigid tubing string or pipe string. U.S. patent application Ser. No. 08/134,022 discloses a modified version of the apparatus shown in the George et al. `213 patent. In this modified version, the actuating mechanism of the gun hanger is modified so that it is operated by a simple reciprocating motion of the coiled tubing string without the need for any rotating motion. Also, a pressure responsive release mechanism connects the coiled tubing string to the perforating gun so that after the gun hanger has been set within the casing, pressure within the coiled tubing string may be increased to release the coiled tubing string from the perforating gun, thus allowing the coiled tubing string to be retrieved prior to firing of the perforating guns.
While both of the previously described apparatus work well, in some well situations problems may occur. For example, when there is an insufficient rathole below the well formation to drop the entire gun assembly a portion of the gun assembly may interfere with flow of fluids from the perforated formation. The present invention solves this problem by providing a modular gun system in which only the sections that remain across the perforations after firing need to be retrieved. In many completions, coiled tubing can be run and retrieved under pressure as a means to fish the gun modules. The modules can be short enough to be lubricated out at the surface which allows removal without killing the well. Of course, a rigid tubing string or pipe string could also be used instead of coiled tubing.
There also may be a need to add additional perforations to an already live well. Many times after a well has produced for some time, the flow weakens to the point that additional perforating is needed without killing the well. With the modular gun system of the present invention, the guns can be lubricated into the well under pressure so that after all of the modules in place, the entire gun assembly can be fired at once.
There may be further occasions when all of the guns do not fire. When this occurs, the fired guns can be retrieved, thus recovering the failed section and allowing easy replacement of it with a new module.